Back to EveryPatent.com
United States Patent |
5,660,617
|
Hatton
|
August 26, 1997
|
System and method for maintaining multiphase flow with minimal solids
degradation
Abstract
An apparatus and method for maintaining continuous flow in a closed loop
test system, of a multiphase composition such as that utilized and
obtained from oil and gas wells and the like. The method and system
provide a test structure whereby a study of the changes in a multiphase
composition (gas/liquid/solid) flow can be studied. Specifically, the
method and apparatus provide for pressure boosting the gaseous components
of the multiphase composition after separation from the liquid and solid
components of the system. A hydrostatic head through which the liquid and
solid components flow provides the necessary potential energy-kinetic
energy exchange such that when the pressure boosted gas is recombined with
the downcomer liquid/solid components, continuous flow of the multiphase
composition is maintained. Pressure and temperature controls permit the
accurate maintenance of pressure, temperature and flow conditions so as to
imitate a real-world environment for multiphase composition flow.
Inventors:
|
Hatton; Gregory John (Kingwood, TX)
|
Assignee:
|
Southwest Research Institute (San Antonio, TX)
|
Appl. No.:
|
648625 |
Filed:
|
May 16, 1996 |
Current U.S. Class: |
95/254; 73/438; 73/861.04; 95/258; 96/204; 96/206 |
Intern'l Class: |
B01D 019/00 |
Field of Search: |
95/256-258,254
96/188,204,206
73/438,861.04
|
References Cited
U.S. Patent Documents
2451604 | Oct., 1948 | Barnes | 73/438.
|
2751031 | Jun., 1956 | Smith et al. | 95/258.
|
2952152 | Sep., 1960 | Fisher et al. | 374/24.
|
2971604 | Feb., 1961 | Lowery | 96/204.
|
3377778 | Apr., 1968 | Gaertner | 96/204.
|
3432992 | Mar., 1969 | Moore | 95/258.
|
3690184 | Sep., 1972 | Chadenson | 73/438.
|
4216089 | Aug., 1980 | Boon et al. | 95/254.
|
4274283 | Jun., 1981 | Maus et al. | 73/152.
|
4352680 | Oct., 1982 | Hackler | 95/258.
|
4369047 | Jan., 1983 | Arscott et al. | 95/258.
|
4508545 | Apr., 1985 | DeLoach | 96/204.
|
4660414 | Apr., 1987 | Hatton et al. | 73/61.
|
4708793 | Nov., 1987 | Cathriner et al. | 96/188.
|
4752306 | Jun., 1988 | Henriksen | 95/258.
|
4760742 | Aug., 1988 | Hatton | 73/861.
|
5251488 | Oct., 1993 | Haberman et al. | 73/861.
|
5394339 | Feb., 1995 | Jones | 364/510.
|
Foreign Patent Documents |
9704/27 | Jul., 1928 | AU | 95/258.
|
619617 | May., 1961 | CA | 95/258.
|
Primary Examiner: Chiesa; Richard L.
Attorney, Agent or Firm: Gunn, Lee & Miller, P.C.
Claims
I claim:
1. A system for circulating a multiphase composition of fluids, solids and
gases continuously around a conduit loop with minimal degradation of the
solids within the multiphase composition, comprising:
a conduit loop test section;
a separator, said separator removing a majority of said gas components of
said multiphase composition from said liquid and solid components of said
multiphase composition;
at least one downcomer conduit, said downcomer providing a hydrostatic head
to facilitate circulation of said fluids and said solids around said loop;
a compressor, said compressor pressure boosting said gas components; and
a recombination riser, said riser recombining said compressed gases and
said downcomer fluid and solid combination, said recombination serving to
maintain and boost overall multiphase composition flow within said loop
test section.
2. The system of claim 1 further comprising a heat exchanger for
controlling a temperature of said compressed gas.
3. The system of claim 1, wherein said at least one downcomer comprises a
plurality of downcomer conduits of one or more diameters such that an
overall downcomer capacity can be selected by alternately permitting or
restricting flow within each of said downcomers.
4. The system of claim 1, wherein said recombination risers are in flow
connection at a plurality of points such that variations in the effective
hydrostatic head for said system can be selected.
5. A method for circulating a multiphase composition of fluids, solids and
gases continuously around a conduit loop with minimal degradation of the
solids within the multiphase composition, comprising the steps of:
separating said gaseous components of said multiphase composition from said
liquid and solid components of said multiphase composition;
drying said gaseous components of said multiphase composition;
pressure boosting said gaseous components;
maintaining said pressure boosted gaseous components at a preselected
temperature through a heat exchanger;
permitting a flow of said liquid and said solid components of said
multiphase composition by drawing said components by gravitational forces
through at least one downcomer conduit;
recombining said pressure boosted gaseous components with said downcomer
drawn liquid and solid components of said multiphase composition in a
recombination riser conduit; and
continuing a flow of said recombined gaseous and liquid/solid components of
said multiphase composition through a test loop section;
wherein said recombination risers serve to maintain a continuous flow of
said multiphase composition through said test loop section.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to systems and methods for
circulating a mixture of fluids, solids, and gases around a flow loop for
testing purposes. More specifically, the present invention relates to a
system and a method for providing the pressure boost necessary to maintain
the circulation of a mixture of fluids, solids, and gases around a
multiphase flow loop with minimal shearing, cutting, smashing, or other
alteration of the solids during the pressure boosting process and the
maintenance of an accurate simulation of long, multiphase flow, conduit
conditions.
2. Description of the Related Art
The design of long conduit multiphase flow systems depends upon an accurate
understanding of the behavior of the various liquid, solid, and gaseous
components of the flow over time. Test systems designed to imitate real
world long conduit flow have generally failed to provide an environment
where such an accurate analysis can be achieved.
Multiphase (gas/liquid/solid) flow test loops generally consist of a
conduit loop test section, a separator to remove most of the gas from the
liquid and solid components, a gas compressor, a pump for maintaining the
flow of the liquid stream with entrained gases and solids, controllers and
meters for the liquid stream (with entrained gases and solids), and a
mixing section for recombining the pressure boosted components upstream of
the loop test section. In some cases, following the test section, the flow
stream is heated to melt the solids, the liquid and gas components are
then separated, and later recombined downstream of the pressure boosting,
flow controllers, meters, and temperature controllers.
When delicate solids are present in a multiphase flow stream, the
consequences of pumping the liquid stream (with entrained gases and
solids) may be undesirable. In particular, the pressure boosting pump may
cut, shear, crush, or otherwise alter the character of the solids. To
reduce this problem, pumps with the least solids destructive behavior are
selected and the length of the loop is increased, thereby reducing the
number of times a particular solid passes through the pump while
traversing a given length of test section.
When studying the growth, agglomeration, and other characteristics of
solids transport, it is of considerable value to significantly reduce pump
degradation. The present invention is directed to providing pressure
boosting to circulate multiphase flow components around a test loop
without requiring the liquids and solids to pass through a traditional
pump. Past efforts along these lines have not been successful.
U.S. Pat. No. 2,451,604, issued to Barnes on Oct. 19, 1948, describes an
apparatus for maintaining multiphase flow and for measuring the density of
a thixotropic fluid such as the drilling mud used in the rotary drilling
of wells. In the Barnes invention, mud is diverted from the flow stream
and is passed through a chamber that establishes a vertical hydrostatic
head whose pressure differentials are measured through a standard
mercury-based pressure sensor.
U.S. Pat. No. 2,952,152, issued to Fisher et al. on Sep. 13, 1960,
describes a gel point indicator directed to identifying the temperature at
which a fluid gels. The apparatus describes a vertical column (similar in
some respects to a vertical hydrostatic head structure) that provides the
necessary cooling for the system but otherwise involves no continuous flow
of a fluid.
U.S. Pat. No. 3,690,184, issued to Chadenson on Sep. 12, 1972, describes an
apparatus for statistically measuring the average density of a liquid
circulating in a pipeline. Fluid is diverted into a column and the density
is measured by comparing the hydrostatic pressure between the column and a
reference column.
U.S. Pat. No. 4,274,283, issued to Maus et al. on Jun. 23, 1981, describes
an apparatus and method for measuring fluid gel strength such as that for
drilling mud. In this system, the flow of drilling mud through a conduit
is interrupted and a differential pressure between various points in the
flow is measured.
U.S. Pat. No. 4,660,414, issued to Hatton et al. on Apr. 28, 1987,
describes a petroleum stream monitoring system and method wherein a crude
oil production stream flows through a separating device to remove
substantially all gas components. Various parameters are measured in this
system including temperature, gas velocity, liquid flow, etc., thereby
providing indications of gas, oil, and water flow rates through the
multiphase system.
U.S. Pat. No. 4,760,742, issued to Hatton on Aug. 2, 1988, describes a
multiphase petroleum stream monitoring system and method similar to the
'414 Hatton patent and also discloses a gas separation means.
U.S. Pat. No. 5,251,488, issued to Haberman et al. on Oct. 12, 1993,
discloses a multiphase volume and flow test instrument wherein fluid is
diverted into a test section and either allowed to separate into its
various phase components or chemically aided in this process. Floats
within the apparatus, tuned to the densities of the various components,
are used to determine the relative quantities of those components within
the flow.
U.S. Pat. No. 5,394,339, issued to Jones on Feb. 28, 1995, describes an
apparatus for analyzing oil well production fluid wherein the fluid is
diverted to a test pipe where various phase components are measured.
Most of the previous attempts to analyze, measure, and regulate the flow of
fluids in a system for the purposes of testing and evaluation, have
focused on specific efforts to identify the relative composition of the
flow compounds and/or to separate the various components at points in the
flow for specific analysis and study. Efforts to accurately simulate the
environment within which fluids must perform in actual field conditions
have been limited and inadequate in most situations. In almost every
instance, the effort to accurately simulate a long conduit flow for fluids
has failed to recreate accurately the flow environment for such fluids.
This failure relates to the inability to appropriately control and sustain
the multiphase composition of the fluid at the same time as the flow
itself is being maintained constant. Well known methods for maintaining
flow generally work against the maintenance of a consistent and constant
liquid/gas/solid composition.
It would be desirable, therefore, to have a system that imitates the
environment within which fluids are likely to flow in real case scenarios
and yet provide such a system with a closed loop structure on a limited
dimensional scale that will make the testing and analysis practical. Such
a system would have to be able to separate the components, boost the
pressure in each of the components to maintain flow, and recombine the
components in such a way that the composition of the flow after pressure
boosting is as close as possible to the composition prior to such actions.
SUMMARY OF THE INVENTION
The present invention overcomes the destructive nature of current
state-of-the-art multiphase loops by pressure boosting the flow components
via a method and apparatus in which the liquids and solids flow at rates
less than, and in piping similar to that of the loop test section.
The complete flow loop of the present invention may be considered to have
two parts: a test section, and a separation/pressure boosting section. The
detailed structures of the test section are designed to provide the
desired testing environment. The separation/pressure boosting section is
composed of an apparatus which adequately separates gas from the flow, a
predominantly liquid filled downcomer array, and a section in which the
pressure boosted gas is recombined with the rest of the flow stream. In
the examples discussed below, the separation section is composed of piping
similar to that of the test section, the downcomers are of a diameter the
same, or smaller than the test section, and the flow in the recombination
section is at a velocity no greater than that of the test section.
In the present invention, the driving (pressure boosting) mechanism for the
liquid and solid components is the hydrostatic head of the downcomer
array, and the driving mechanism for the separated gas is the compressor.
Since the in situ velocity of the liquid and solid components is lower in
the downcomers than in the test section, the solid components sustain
little degradation in the downcomer array. The solid component's pressure
boosting thus occurs under conditions very similar to flow in a pipeline.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 discloses in schematic form the fundamental components of the flow
loop and pressure boosting system of the present invention.
FIG. 2 discloses a detailed cross-sectional schematic view of the separator
and a plurality of downcomers utilized in the system of the present
invention.
FIG. 3 is a perspective schematic drawing showing the elements of the
present invention as they would be incorporated to scale in a fluid flow
test system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is made first to FIG. 1 for a detailed description of the
fundamental components of the multiphase flow loop of the present
invention. It should be noted that FIG. 1 is intended to schematically
show the complete flow loop of the present invention but does not
necessarily disclose the actual vertical or horizontal positions of the
elements. Once again, the goal of the system of the present invention is
to simulate the conditions that production fluids and other multiphase
fluids would experience in real world operation. This is accomplished by
providing a conduit for the multiphase fluid flow whose dimensions balance
the need for a long flow path and the need for a confined testing
apparatus. Conduit (10), shown in FIG. 1 schematically as a small section
of conduit, represents a test section of conduit that is much shorter in
overall length than the long distance flow lines to be simulated. It is
not unusual in deep water production environments for fifty-mile long flow
lines to be installed or planned. Clearly, the installation of such a
lengthy flow line for testing purposes is impractical, so a scaled down
test section, such as in the quarter-mile loop in the preferred embodiment
of the present invention for example, is utilized instead. As long as
other factors involving the pressure boosting and temperature can be
controlled, the quarter-mile loop test section provides an appropriate
imitation of the longer flow lines in real world applications.
Test section (10) receives the recombined multiphase flow from commingling
columns (12) and (14). Column (12) carries the liquid and solid components
of the multiphase fluid which are then combined with the gas component of
the multiphase flow from column (14). This recombination of the
fluid-solid component in column (12) with the gas component in column (14)
is carried out by way of valves (16) and (18). The use of two valves (16)
and (18) serves to permit variations in the rate and manner in which the
gas is recombined with the fluid-solid flow. The vertical rise of the gas
experienced from either valve (16) or valve (18) contributes to the flow
rate of the overall system.
Once the liquid, solid and gas components of the multiphase fluid are
recombined at point (20) in the flow loop, the multiphase fluid is
characterized with pressure sensor (22) and temperature sensor (24). Test
section (10) may be isolated from the pressure boosting components of the
system by closing valve (26) and (36). When valves (26) and (36) are open,
the flow rate in test section (10) is measured by flow meter (28). Test
section (10) is generally maintained to imitate variations from the
horizontal typically found in long line conduits utilized with off-shore
production. Immediately prior to separating the multiphase components for
pressure boosting, a declination section (30) from the horizontal is
placed in the test section (10) such that the separation process,
especially as between the gaseous elements and the liquid/solid elements,
is smoothed out. Such a declination angle (30) provides a natural
separation between the heavier liquid/solid components and the lighter
gaseous components. Temperature and pressure of the multiphase fluid flow
are again measured at this point with temperature sensor (32) and pressure
monitor (34). The multiphase flow moves into the separator section through
conduit section (38).
The specific configuration of the separator is described in more detail
below with respect to FIG. 2, but the general components can be seen in
FIG. 1. The separator comprises a terminal end (40) of flow loop (10)
which directs the multiphase components either into gas manifold (42) or
downcomer array (46). Downcomers (46) are controlled by an array of valves
(48), while gas manifold (42) is controlled by valve (44).
Downcomers (46) terminate in conduit section (50) which is provided with a
drain valve (52) for evacuation of downcomer array (46). Fluid may be
added to the system through conduit (54) which connects with conduit
section (50). As the fluid/solid components of the multiphase flow system
move back toward the test section, the pressure and temperature are again
measured with pressure sensor (56) and temperature sensor (58). Flow moves
through valve (60) which leads into commingling conduit section (12). A
second drain port is controlled by valve (62) that permits the evacuation
of commingling section (12).
The gas in the flow is drawn away from the separator through gas manifold
(42), through valve (44), and into scrubber (64). Scrubber (64) removes
any remaining liquid and solid components through conduit (66) and ducts
these back into the flow stream at conduit section (38). The gas
components leave scrubber (64) by way of conduit (68) and are pressure
boosted in compressor (70). These pressure boosted gas components are
ducted from compressor (70) to heat exchanger (74) by way of conduit (72).
Heat exchanger (74) maintains an appropriate temperature on the gaseous
elements. In the test section and the separator/pressure boosting section,
well known pipe external temperature controlling systems are used to
maintain the temperature in the overall multiphase flow fluids. Pressure
and temperature are sensor (76) and temperature pressure sensor (76) and
temperature sensor (78). Gaseous flow is measured with flow meter (80) and
is controlled through valve (82). Gas flow back into the test system is
made through conduit (84), which leads to commingling conduit (14) as
described above.
In a preferred embodiment of the present invention, conduit (10) is a
three-inch pipe that opens into a six-inch manifold (42). Gas line
components (68), (72) and (84) are three-inch conduits in the preferred
embodiment. Liquid riser (12) and gas riser (14) are likewise each
three-inch conduits in the preferred embodiment. Downcomers (46) vary in
diameter as described in more detail below.
Reference is now made to FIG. 2 for a description of a detailed view of the
separator component of the present invention. Separator (42) has an inlet
from the test loop conduit (not shown) by way of declination section (30).
The multiphase fluid (106) moves down through angled conduit section (30)
to separator manifold input (38). Conduit (30) is angled down to
facilitate the separation between the gaseous elements in the multiphase
flow and the fluid and solid elements which are directed down in the
angled conduit section (30). Separator manifold (42) is comprised of a
plurality of downcomers (46a-d) and a plurality of gaseous manifold ducts
(102). Gaseous manifold ducts (102) join together into gas outlet conduit
(41) where the gases are eventually directed to scrubber (not shown) by
way of conduit (43).
Separator (42) terminates at one end in manifold terminal cap (40). Each
downcomer (46a-d) incorporates a valve (48a-d) that permits the number and
diameters of the downcomers to be varied according to the requirements of
the test. Downcomer (46a) and (46b) are three inches in diameter in the
preferred embodiment, while downcomer (46c) is two inches and downcomer
(46d) is one inch in diameter. A large variety of total diameters are
possible given this combination of downcomer pipe diameters.
Separation of the gas from the multiphase fluid occurs both in the manifold
itself and in the downcomers which allow the gaseous elements to rise
vertically upward even as the multiphase fluid flows down. Taylor bubbles
(104) rise up through the multiphase fluid (100) as circulation in the
system is maintained. The gaseous components are drawn off through the
manifold and carried to the scrubber (not shown) where the final drying of
the gas occurs. As indicated above with respect to in FIG. 1, any
remaining liquids found in the gas are ducted back into the flow steam
prior to the separator shown in FIG. 2.
Reference is now made to FIG. 3 for a detailed description of a perspective
view of a scale-accurate schematic of a test setup utilizing the present
invention. Most of the components disclosed in FIG. 3 are identical to
those described in FIG. 1, but are shown in a more appropriate scale. Test
section (10) is, as indicated above, a three-inch diameter conduit of a
quarter-mile in length in the preferred embodiment that provides a flow
line for the fluids under test. Declination conduit (30) begins the
separation process at separator (42). Downcomers (46) draw off most of the
liquid/solid components of the multiphase fluid while the gaseous
components are ducted off into scrubber (64). Conduit (66) returns the
remaining liquid and solid components from scrubber (64) back into the
multiphase flow stream. Compressor (70) takes the gaseous components from
scrubber (64) and boosts the pressure on these components. Heat exchanger
(74) modifies the temperature of the gas components. Conduit (84) returns
the pressurized and temperature-controlled gas to riser (14) where it is
combined with the liquid and solid components of the multiphase fluid in
riser (12). The combination of risers (12) and (14) are generally referred
to as recombination system (13). Downcomers (46) which may be selectively
activated as described above, draw the solid and liquid components down to
a position where they are carried up through riser (12). Liquid injection
line (54) allows appropriate access for adding multiphase fluid to the
system.
In the embodiment of the present invention shown in FIG. 1. Pressure
boosting of the separated gas stream is provided by an ordinary gas
compressor. Following this compression, the gas is optionally metered
and/or cooled to an appropriate temperature before being recombined with
the rest of the flow stream. Pressure boosting of the non-separated
components (primarily liquid/solid) is provided by the hydrostatic head of
the downcomers. After the metering of the components, the compressed gas
and other components are commingled in the recombining section. Pressure
drop elements (hydrostatic head, frictional pressure drop, acceleration,
and other energy losses) in the test section are balanced with those in
the separator and downcomers. This balance, together with the compression
of the gas component provides the drive for circulating all of the
components through the test section. Several gas commingling ports are
provided to allow additional control.
The separator should be designed so as to provide (a) sufficient gas
separation, (b) a liquid/solid stream suitable for metering if desired,
and (c) minimal solids accumulation or agglomeration. In many cases, it
may be desirable to also control the temperature of the separator. For
example, with paraffins and hydrates, it may be desirable to maintain the
separator temperature at or just above the temperature of the stream
flowing into the separator.
If the solids and liquids are of equal density, then a suitable design for
the separator is fairly straightforward. Usually, however, not all of the
liquids and solids have the same density. In this case, the separator
should be designed (and is designed in the preferred embodiment) to pass
rather than accumulate the solid components. In addition, it is important
to design the separator so as to not promote agglomeration of one of the
solid components. In the system of the present invention, the downcomers
are sized such that none of the liquid or solid components will accumulate
in the separator and such that gas carry under is limited. For example,
for gas, water, and ice flow, the system should be designed to pass all of
the ice in a timely fashion with minimal gas carry under. The density of
water, ice and gas might be 1, 0.9, and 0.09 gm/cc, respectively. The
downcomer should then be designed such that the ice particles are drug
down but gas bubbles greater than a given diameter are not. One possible
design is that for which gas Taylor bubbles rise and ice particles carry
under. For example, the velocity of a gas Taylor bubble, V.sub.Taylor, is
often given by
V.sub.Taylor =V.sub.mixture +0.35*(g*d).sup.0.5
where V.sub.mixture is the overall mixture velocity. For a 4-inch internal
diameter pipe the mixture velocity corresponding to a Taylor bubble
velocity of zero is
V.sub.mixture =-0.35*(32/3).sup.0.5 =-1.14 ft/sec
or about 45 gal/min. Assuming a 25% gas carry under, this provides a system
with a maximum liquid and solid volumetric rate of 34 gal/min per 4-inch
downcomer (or a superficial velocity of about 0.85 ft/sec). The minimum
rate per 4-inch downcomer may be calculated from the solids and liquids
density differences, fluid properties, and solids and droplet sizes.
Generally, the relevant solid to liquid density ratio is between 0.7 and
1.3 as compared to the gas to liquid density ratio of less than 0.1.
Because of this, there is usually a turndown ratio of 2.5 to 2 for each
downcomer. Smaller diameter downcomers may be used to further reduce the
minimum rate. Multiple downcomers (as disclosed in the preferred
embodiment) allow a large maximum flow rate. At low and intermediate rates
some of the downcomers may be valved off. With a 2-inch, a 3-inch, and
2@4-inch downcomers, such a system could provide a superficial liquid and
solid flow rates from 0.1 to 5 ft/sec in 4-inch pipe.
By suitably choosing the height of the downcomers and the resulting
hydrostatic head such a system can be readily designed to provide a
sufficient drive to continually circulate the fluids through the test
section.
While the method and system of the present invention have been described,
it is anticipated that one skilled in the art would identify further
applications of the present invention in a manner consistent with the
procedures associated with the present invention. For example, both the
pipe diameters and the pipe lengths identified in the description of the
preferred embodiment may vary significantly according to the requirements
of the test parameters.
It is anticipated that the present invention would have applications in any
environment where maintaining a multiphase flow with minimal solids
degradation is required.
Again, it is understood that other applications of the present invention
will be apparent to those skilled in the art upon a reading of the above
description of the preferred embodiments and a consideration of the
appended claims and drawings.
Top